With the popularity of portable communication devices, such as smart phones and so forth, numerous fabrication technologies are geared towards electronics miniaturization and densification. Embedding techniques are widely used in substrates of the communication devices. For instance, embedding a high thermal conductor component in the substrate will provide a low resistance heat path to thermal ground. In addition, the embedding techniques may also provide an attractive interconnect solution without wire bonding for improved electrical performance, and offer the potential to reduce manufacturing cost for complex products.
In communication devices, radio frequency (RF) filters are key components to determine electrical performances. Typical filter solutions for RF and microwave frequencies include discrete filters, coupled line filters, cavity filters, and acoustic filters. Due to their small size, high Q values, and very low insertion losses at microwave frequencies, the acoustic filters (including Bulk Acoustic Wave (BAW) filter and Surface Acoustic Wave (SAW) filter) are highly desired in modern communication applications. Conventional dielectric loaded resonator-based filters may achieve high Q factors, but require very careful manufacturing processes with exacting mechanical alignment requirements. Sometimes, the resonators in the conventional dielectric loaded filters tend to lose mechanical alignment in field service with their properties shifting with time and environmental conditions, thereby severely impacting system level performance. In addition, the dielectric resonators may need to be manually tuned after fabrication, which significantly increases production cycle time and cost. In the case of acoustic filters, though there is no need for mechanical alignment, each frequency band of the acoustic filter may require a specific resonator structure, which significantly limits the scalability of such filters.
Accordingly, there remains a need for improved substrate and resonator designs, which utilize the advantages of embedding techniques in substrates and solve the alignment and scalability issues. Further, there is also a need to keep the final product cost effective without increasing fabrication complexity.